I added the following, but it does not show the window of WebEngineView in my main.qml.

#include <QtGui/QGuiApplication>
#include <QtQml/QQmlApplicationEngine>
#include <QtWebEngine/qtwebengineglobal.h>

int main( int argc, char *argv[ ] )
{
QGuiApplication app( argc, argv );

QtWebEngine::initialize( );

QQmlApplicationEngine appEngine;
appEngine.load( QUrl( "qrc:/main.qml" ) );

return app.exec();
}

It means I have no need of a main.cpp?

This is my main.qml:
import QtQuick 2.4
import QtWebEngine 1.0
import QtQuick.Window 2.0

WebEngineView {
width: 1200
height: 900
visible: true

url: 'http://duckduckgo.com'
//Component.onCompleted: loadHtml( "<html><body><p id='demo'></p><script>document.getElementById('demo').innerHTM L = navigator.userAgent</script></body></html>" )
}

and this is my main.cpp:
#include <QtGui/QGuiApplication>
#include <QtQml/QQmlApplicationEngine>
#include <QtWebEngine/qtwebengineglobal.h>

int main( int argc, char *argv[ ] )
{
QGuiApplication app( argc, argv );

QtWebEngine::initialize( );

QQmlApplicationEngine appEngine;
appEngine.load( QUrl( "qrc:/main.qml" ) );

return app.exec();
}

What's wrong? It doesn't show anything.